1. Field of the Invention
The present invention relates to an electric motor driving a compressor used for an air conditioner or a freezer, in particular, to a stator iron core of the electric motor and a method for manufacturing the stator iron core of the electric motor.
2. Description of the Related Art
FIG. 13 is a plan view of a conventional stator of an electric motor disclosed by the same applicant in Japanese Patent Application No. 11-020128. In the figure, a reference numeral 3 shows a plate-shaped core segment (magnetic pole segment) made of magnetic material. At one end of the magnetic pole segment, a concave portion 3a and a convex portion 3b are formed on both surfaces as a connection means. At the same time, an end face 3c of the magnetic pole segment having an arc shape (male shape) is formed on a circumference of a circle having the same center as the center of the concave portion 3a and the convex portion 3b. At the other end of the segment, an end face 3d having an arc shape (female shape) is formed so as to be engaged with an end face 3c of an adjoining magnetic pole segment 3. A reference numeral 4 shows a first iron core member in which plural magnetic pole segments 3 are aligned via the end face 3c and the end face 3d. 
FIG. 14 is a cross sectional view taken along the line DD of FIG. 10.
As shown in FIG. 14, a reference numeral 5 shows a second iron core member in which plural magnetic pole segments 3 are aligned in the longitudinal direction (as shown by an arrow X). The first iron core member 4 and the second iron core member 5 are stacked or laminated alternately. In the stacking direction (as shown by an arrow Y), the concave portion 3a of the magnetic pole segment 3 and the convex portion 3b of the adjoining magnetic pole segment are engaged, so that both magnetic pole segments 3 are connected in the longitudinal direction (as shown by the arrow X) so as to rotate around the center of the concave portion 3a and the convex portion 3b in the direction of an arrow R. A reference numeral 6 shows a coil wire wound around each magnetic pole segment 3, and 7 shows an iron core formed circularly by turning the concave portion 3a and the convex portion 3b of each magnetic pole segment 3 made by laminating both iron core members.
In the following, a method for manufacturing the conventional iron core structured as described above will be explained. FIG. 15 shows a magnetic member plate for manufacturing the magnetic pole segment 3.
As the first step for processing the first iron core member 4, surrounding portions of the both end faces 3c and 3d are formed by punching (or stamping) out portions shown by a real line within a hatched portion at a location indicated by an arrow A in FIG. 15. As the first step for processing the second iron core member 5, surrounding portions of the both end faces 3c and 3d are formed by punching portions shown by a real line within a hatched portion at a location indicated by an arrow B in FIG. 15. By the above punching operation, the concave portion 3a and the convex portion 3b, which can be engaged with each other, are formed on both surfaces of the end portions, on which the arc end face 3c of the magnetic pole segment 3 are made as shown in FIG. 16. At the same time, a hole portion 3h is formed on the magnetic pole segment 3 of the top layer so as to be engaged with the convex portion 3b of the magnetic pole segment 3 of the lower layer.
Next, at a location indicated by an arrow C in FIG. 15, the first iron core member 4 and the second iron core member 5 are formed by serially and alternately punching a portion shown by a real line within a hatched portion, that is, a surrounding portion of the both end faces 3c and 3d, which are formed at the location indicated by the arrow A, and a surrounding portion of the both end faces 3c and 3d, which are formed at the location indicated by the arrow B. These iron core members 4, 5 are sequentially and alternately stacked or laminated within a metal stacker.
Subsequently, the coil wire 6 is wound, and the iron core 7 can be circularly formed by turning the concave portion 3a and the convex portion 3b, which are engaged in the laminating direction, of each magnetic pole segment 3.
FIG. 17 shows a part of the iron core which has been circularly formed. In FIG. 17, 2 shows a slot which is a space for winding the coil wire 6. Further, 2a shows a bottom portion of the slot 2 which has an angular portion made by abutting straight line portions 2b of the magnetic pole segment 3 and of the adjoining magnetic pole segment 3. In FIG. 17, the coil wire 6, which exists, is not illustrated for clarifying the explanation.
FIGS. 18 and 19 show a conventional stator iron core of an electric motor disclosed by the Japanese Unexamined Patent Publication No. HEI 9-191588. As shown in FIG. 18, predetermined pieces of magnetic material are staked or laminated, in which plural magnetic pole segments 101 are connected via a thin connection portion 102. Confronting surfaces 102a and 102b of the connection portion are provided on both sides of the thin connection portion 102. Further, confronting surfaces 101b and 101c are provided on ends of the magnetic pole segments 101 located at far ends. The confronting surfaces 101b and 101c have the same shape as the confronting surfaces 102a and 102b. 
A coil wire (not shown in the figure) is would around each magnetic pole segment in the stator structured above. As shown in FIG. 19, each thin connection portion 102 is bent, the confronting surfaces 102a and 102b of the connection portion located on both sides of the thin connection portion 102 are joined, and finally, the confronting surfaces 101b and 101c of the end portions are joined to circularly form the stator iron core of the electric motor.
The conventional stator iron core of the electric motor is structured as shown in FIG. 13. The bottom portion 2a of the slot 2, which is made by circularly forming the stator iron core, has a fine angle as shown in FIG. 17, so that the stress of the load is concentrated to that angular portion when the load is applied to the bottom portion on circularly forming the iron core 7. Further, when the electric motor is mounted in a compressor, etc. by fixing into a housing and the like of the compressor with shrink-fitting (to insert the electric motor into the expanded housing by heating) or press-fitting (to insert the electric motor into the tight housing by pressure), the fixing force is concentrated to the angular portion. Accordingly, the performance of the magnetic material is reduced, which causes problems that the efficiency of the electric motor is reduced, it becomes difficult to keep a sufficient stiffness, and further, vibration or noise may be generated during the driving of the electric motor.
The conventional stator iron core of the electric motor is structured as shown in FIG. 13. Accordingly, when the electric motor is mounted in the compressor by fixing in the housing and the like with shrink-fitting or press-fitting, an outer circumference of the stator iron core around the concave portion 3a and the convex portion 3b, which rotate when the iron core is circularly formed, may contact with an inner perimeter of the housing. This means the stator iron core tend to be influenced by the dimensional precision of the housing and the like, namely, a circularity of the outer circumference and the inner circumference of the stator iron core of the electric motor tends to become worse by the contact force at the time of shrink-fitting or press-fitting. Further, when the circularity becomes worse, an air gap between the stator and the rotor becomes irregular at the time of driving the electric motor. This may generate magnetic unbalance of the electric motor, and also causes a problem to generate noise or vibration.
The conventional stator iron core of the electric motor is structured as shown in FIGS. 18 and 19. Accordingly, the confronting surfaces 101b and 101c of the end portions are easily dislocated in the radius direction at the time of circularly forming the stator, which makes it difficult to keep the mechanical precision of the stator. Therefore, when the stator is assembled in the electric motor, the magnetic performance of the magnetic material is decreased to cause problems that the efficiency of the electric motor becomes worse, the magnetic unbalance may be generated, and vibration or noise may be generated on driving the motor.
Further, in the above example, the connection portion is made thin. Even if the connection portion is made bendable by some means in the stator, the confronting surfaces 101b and 101c of the end portions are easily dislocated in the radius direction, which causes the same problem as above.
Further, in the above example, the confronting surfaces 102a and 102b of the connection portion and the confronting surfaces 101b and 101c of the end portions have a straight line portion. Even if the portions have an arc portion, the confronting surfaces 101b and 101c of the end portions are easily dislocated in the radius direction, which causes the same problem as above.